Multiple stand roller mill with worm and worm wheel drive to each roll



Oct. 2, 1951 T. G. cEcKA MULTIPLE STAND ROLLER MILL WITH WORM AND WORMWHEEL DRIVE TO EACH ROLL 5 Sheets-Sheet 1 Filed Jpn. 50, 1947 THOMAS ZEC /ZZ A 7- TOPNE s Oct. 2, 1951 T CECKA 2,569,744

MULTIPLE STAND ROLLER MILL WITH WORM AND WORM WHEEL DRIVE, TO EACH ROLL'5 Sheets-Sheet 2 Filed Jan. 50, 1947 /NI/NTOR THOMAS G. 65cm A TTORNErs Oct. 2, 1951 'r. G. CECKA MULTIPLE STAND ROLLER MILL WITH WORM 7 ANDWORM WHEEL DRIVE TO EACH ROLL Filed Jan. '30, 1947 5 ShaetsSheet 5 L M 37 II I. III

lM/ENTM THOMAS G. CEc/m MWM ATTZZQNEYS T. MULTIPLE STAND Oct. 2, 1951 e.CECKA ROLLER MILL WITH WORM AND WORM WHEEL DRIVE TO EACH ROLL 5Sheets-Sheet 4 Filed Jan. 50, 94?

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MULTIPLE STAND ROLLER MILL WITH WORM AND WORM WHEEL DRIVE TO EACH ROLLFiled Jan. 30, 1947 5 Shuts-Sheet 5 INVENTOR. 7710/14/15 G. 55004 621,WM MW A TTOHNE rs Patented Oct. 2, 1951 MULTIPLE STAND ROLLER MILL WITHWORM AND WORM WHEEL DRIVE TO- EACH ROLL Thomas G. Cecka, Minneapolis,Minn, assignor to International Milling Company,

Minneapolis,

Minn, a corporation of- Delaware Application January 30, 1947, Serial N0. 725,392 6 Claims. (Cl. 241-135 This invention relates to roller millsand more particularly to improvements in the construction of rollermills of the type used, in the milling of dry, pulverulent material,such as grain, feeds, mill products, salts, pharmaceuticals and thelike.

Roller mills have long been used for the breaking and milling of drymaterial, and in the grain milling and other industries have been widelyused in batteries of many mills operating in parallel. In suchinstallations it has been common to provide a line shaft for supplyingpower to a battery of mills, each mill or mill stand, as it is sometimesdesignated, being driven by a belt to the common line shaft, and themills have been designed to accommodate such drives.

While these mill installationsare satisfactory and have served to millcountless tons of materials they are subject tomany serious defects dueto the type of installation required and due to their inherentmechanical construction.

One of the most serious defects in the common belt driven mill standarises out of the common drive; Since all mills were of necessity beltedto a common line shaft any operational defect necessitating servicing ofone mill has frequently required a shut-down of the entire drive shaftand all mills connected to it. Furthermore, the belt drive itself, hasinvolved relatively short belts withv consequent highbelt tensions inorder to deliver the required horsepower, and this has led to defects inoperationvoccasioned by bearing failure, misalignment of the roll,damaged rolls, etc. In addition, heavy stress of the belts istransferred from the mill to the building in which it. is housed.

It is an object of the present invention. to provide an improved rollermill wherein an individual drive is' provided for each mill andfurthermore to provide an improved gear drive between the motive powersource and the several slow and fast rolls of the mill.

Other defects of the present mills have arisen out of their constructionwherein the cooperating fast and slow rolls are situated at equallevels. In such roller mills the entire thrust of the rolls, occasionedby the pressure of the-material being milled between them, has had to becarried by the roll shaft bearings and this bearing load, taken with theadded load due to belt tension of the drive, has been the cause offrequent operational di'fficulties. It is an object of the presentinvention to provide an improved roll mill wherein the thrustdue tomaterial pressure on the rolls while milling is at least partiallycompensated by theweight of the roll itself so as to relieve in partthe'excessive load on the bearings of the mill.

Another serious objection to conventional mills is the fire hazard andemployee hazards occasioned by the belt drives employed for driving therolls. It is an object of the invention to eliminate these hazards byproviding a self-contained gear drive unit in which the roll drive beltsare eliminated and which are consequently free from danger due to theignition of dust by static electricity'on' the belt and free from dangerto. employees. It is a further object to provide. an improvedself-contained milling unit wherein all working stresses are within theunit itself and not communicated to the building as with belt drivenmills and which is free from the vibration which has commonly beenencountered due to large rotating pulleys in belt driven mills.

It is also an object of the invention to provide an improved roller millwherein the rolls are driven by direct mechanical gear connectionfrom amotive power source and at the same time provision made for widevariations in adjustment of therolls to compensate for wear of the rollswith efficient gear drive connection being maintained the while.

It is a further object of the invention to provide an improved millwherein the fast roll is positioned above and partially overlying theslow roll so as to eliminate the necessity for tramming the rolls (-i.e. maintaining precise parallelism) under milling conditions. It is afurther object to provide an improved gear drive wherein shortershafting is provided. This reduces bowing of the roll shafts andtorsional strains which were common causes of, failures with the ratherlong roll shafts-needed in belt driven mills.

Other and further objects of the invention are those inherent in theapparatus herein illustrated, described and claimed.

The invention is illustrated with reference to the drawings in whichFigure 1 is a side elevational view of the machine with certain partsremoved;

Figure 2 is an end elevational view taken in:

the direction of arrows 2-2 of Figure 1 showingthe drive gears'exposedand their enclosing housingremoved;

Figure 3 is a sectional' view taken in the direction of arrows 33 ofFigure 1;

Figure 4 is a fragmentary sectional view taken along, the lines and inthe direction of arrows and in the; direction of arrows 4-4 of Figure 1,

illustrating the rolls after they have been reduced in diameter duringtheir service life;

Figure 6 is an enlarged detail of the adjusting mechanism for moving oneof the roll shafts and is representative of the mechanism used foradjusting the ends of the rolls; and

Figure 7 is a fragmentary sectional view through one of the quickthrow-out levers and associated cams.

Throughout the drawings corresponding numerals refer to the same parts.

Referring to the drawings the machine comprises a frame and housinggenerally designated I having end plates II and I2 and side plates I3and I4. The housing may be cast or fabricated of any suitable materialsand is preferably provided with a bolting flange at I5 and I6 by whichthe machine can be bolted to the millingafloor. The upper portions ofthe side plates I3 and I4 converge inwardly at I8 and I9 and thenceareshaped in to form the top 23 which is provided with a header 2I which isin turn attached to the supply chute 22.

The interior space of the housing is provided with upwardly convergingbafies 24-25 which meet at the point 26. These bafiies, together withthe baffle boards 28 and 29, all extend from one end plate II to theother end plate I2 and form interior hoppers so that the material beingfed flows in the direction of arrows 3i] and 3I onto the feed rolls 32and 33. The feed rolls are relatively small diameter and serve almost toclose the bottom spaces 34 and 35 formed by the converging baflies 24-28and 25-29, respectively.

Feed roll 32 is mounted upon the feed roll shaft 36 which is journaledin the end plates II and I2 and extends outwardly beyond rear end plateII and carries a relatively large diameter pulley 38. ,Similarly, thefeed roll 33 is carried upon the shaft 48 which is likewise journaled inthe end plates II and I2 and extends out beyond rear end plate II, asshown in Figure 1, where it carries the pulley 42. Feed roll 32, itsshaft and a shaft 59 carrying a main drive gear 66. Below the housingtunnel there is a central web 56 extending from end plate II to endplate I2 which serves to separate the two streams of milled materialfalling on opposite sides of the housing 55. In some instances thesestreams may be different, and the separation 56 thus permits them to beseparately withdrawn.

Within the main housing there are also positioned two pairs of millingrollers 6I-52 and 3364, each roller being provided with a shaft uponwhich it is journaled. The shaft 65 carries roll BI and extends throughstuffing boxes 85 and 61 in the end plates and is journaled upon pillowblock 68 which is mounted upon end plate II and pillow block 69 which ismounted upon plate I2. Similarly, shaft Ill of roll 63 likewise .extendsthrough the stuffing boxes in the end plates II and I2 and is likewisejournaled in suitpulley rotate in the direction of arrow 43, and

feed roll 33, its shaft and pulley 42 rotate in the direction of arrow44, being belt driven as hereinafter described. Likewise, within thehousing there are a pair of downwardly extending and converging bafiies46 and 41 which extend from the side walls I3 and I4, respectively, andat their lower ends form a chute space 48 which is connected to deliverychutes leading to classifying machinery below the milling floor. Theconverging chute formed by the bafiles 46 and 41 collects the milledmaterial as hereinafter described and thus delivers it from the mill.-

Within the space between the baflies 46 and 4! there is a motor housingenclosure 0r tunnel 50 which extends from end' plate II to end plate I2.The housing has a bottom portion 54 and sides 52 and 53 which convergeupwardly at their top portions 5I--5I at an angle such that the milledmaterial will not lodge thereon. The motor housing tunnel 5D is formedintegrally with the end walls I I and I2 and is suitably supported byinterior bracing not illustrated. The end walls I I and I2 are, ofcourse, provided with opening plates on the ends of the tunnel 50 andthese plates are provided with louvers 55 so as to allow throughventilation from one end to the other for cooling the drive motortherein. The motor 58 which is mounted in tunnel 50 is thus completelyisolated from the milled material falling downwardly within the hopperspace formed between the baflles 46 and 41. From motor 58 there extendsable bearings fastened on the end plates, one of the bearings I2 on endplate I2 being illustrated in Figure 3. The bearings carrying the shafts65 and III and hence the rolls GI and 63, respec-' tively, are journaledupon fixed journals which do not move in respect to the end plates IIand I2. Hence, the axis of rotation of the rolls BI and 63 remains fixedthroughout their service life.

Roll 62 is supported. upon shaft I4 which-likewise extends out throughstuffed boxes in the end plates II and I2 and is supported by journalsI5 illustrated in Figure 3 and a corresponding journal at the other endof the machine. These journals are mounted upon a frame I6 having a T-slot connection to a correspondingly shaped slide TI attached to the endplates and I2. Similarly, roll 54 is mounted upon shaft 19 whichlikewise extends out through suitable stuffing boxes in the end platesII and I2 and is carried by journals mounted upon each end plate, ashereinafter described. One of the journals is illustrated in Figure 3and there is a corresponding journal at the other end of the machine.The journal 80 is likewise mounted upon the frame 8I which has a T-slotconnection to the correspondingly shaped slide 82 which is solidlyfastened to the end plate I2. The journals at each end of the machinecarrying the roll shafts I4 and I9 of rolls 52 and 64, respectively, arethus permitted to move in a plane transverse to the machine, the planebeing at lines 8383. Suitable sliding stufiing boxes are provided ateach end of each shaft I4 and I9 where they pass through the end platesII and I2 and thus keep dust from the milling operation from passing outof the mill around .the shafts. The stufiing boxes are either splitdiametrically or are made so as to lift from the machine frame, so as toallow removal of the rolls and their shafts and gears when the millframe is opened as hereinafter described.

Figure 3 shows the two slides 11 and 82 which are permanently fastenedto end plate I2. Figure 1 shows the slide 82 which carriesjournal 80adjacent end plate I2 and also shows the slide 84 carrying the journal85 at the other end of the machine upon which the shaft I9 is mounted.

It is to be understood, of course, that the journal,

not illustrated adjacent rear end plate I I and at the far end of shaftI4, is likewise mounted upon a slide exactly similar to that shown at ITand 82 in Figure 3. The journal constructions for the shafts I4 and I9and their adjustments hereinafter described are identical at each end ofthe machine and therefore it is only necessary to,

seed-744 describe in detail the. construction adjacent-the end plate I2.

Referrin to Figure 3 the slide TI carries the frame 16' so that theframe 16 carryingthe journal I5 may move ina-translatorymotion back andforth in the direction of the double arrow 86;. Similarly, the slide 8.2which mounts the frame 81 carrying the journal 8!) permits the frame.81: and journal 80 to be moved in the direction of the double arrow81).. Thus, both. the

journals. 7.5.. and 80 can moveback and forth. and.

hence carrying; the shafts I4 and 19. inc. trans.- verse. plane atthelevel of line 8.3-83. The degree of. such, movement: permitted in themachine suflipientto accommodate not: only the desiredop nins. lithe-macn for clearing; an jamsthat may occur, b t also sufiici nta o-permitthe. mov ment of rolls 62 and 64 more closely adjacent the rolls B21 and63;, respectively, so as, to maintain the desired close clearance formilling as, the rollsare reduced in size. during their service life. It.

may be. pointed; out at this juncture that. in ordinary miling practicefor flour milling ma.- chine-ry, the rolls SI and 63, 62 and 64 are:approximately nine inches in diameter as initially manufactured. Therolls may be smooth. or corrugated trough) depending upon the type ofmilling effect desired, As the milling takes place, there is some wearon the roll and it iscustomalsy to. remove the rollsfrom the machinefrom time, totime andre-finish them to true and accurate diameterthroughout their length and to re-corrugate them when. corrugations aredeired. This, cffectsfan overall reduction in the diameter, of the rolland compensatory adjustment must therefore be provided to maintaindesired close clearance for milling. Figure 4 represents the position ofthe rolls set. close as during aniling when the rolls are of maximumdiameter when new. Figure 5 in the full line position illustratestheposition of the rolls. likewise set. close for milling but after theyhave been reduced in diameter during the service life. The dotted linesin Figure 5 illustrate the position of therolls-when they are new andcorresponds thus. to the full lineshowing of Figure 4.

Figure 3- and Figure 6; which is an enlarged view of the mechanism forshaft I 6, illustrate the mechanism for-adjustment of each of the adjustable rolls 62 and 64. For this purpose there is provided a shaft 88and. another shaft coaxial with it at the other end of the machine. Bothshafts are mounted on their adjacent end plates.

Upon the shaft there is mounted an oscillatabl'e lever 89 having ahandle portion 99; the lever carries two eccentrics SI and 92 towhichthere are attachedeccentric links 93 and 94; respectively. Link 93'serves roll 64 and link 23 serves roll 62.

The link 93"has athreaded' connection at95 to the.

rod 96, and rod 96 extends through a cylindrical space 51 in the bearingframe 8| and thence to termination at the hand wheel; I whichis solidlymounted: on rod 96. By turningthe hand wheel Ills the rod may bethreaded more or less into the threaded connection 95. Upon the rod 96there is mounted sleeve IBI which is threaded at IOS' uponthe rod 96.The threads 95 are-fine threads and I are coarse threads. Hence, byrotating rod 98" by means. of hand wheel I00 the sleeve canbe' movedaxially in respect to eccentric. link 93.- A locking nut hand wheel I92is threaded on shaft. 96 at threads I05 and by turning wheel I32. tight,any adjustment of; the sleeve I6! on rod 3% can be fixed. Sleeve II".has a nut. at I185; and an internalcollar at I'U'l. Spring I04 bearsagainst the collar I'DT and against. the end weir I08 of the cylinder-91. By initially turning up nut I08 the spring IMwmay be adjusted toagiven compression. A cover plate IE9 serves as a journal around sleeveMI and closes the.- cy-llne drical space 91. Cover plate i09 is heldonto: the cylinder 91: by. several cap screws.

The hand lever is first. moved against rights hand stop 98; to rollclosed position in which the eccentric links 93- and a4 are moved"towards each other. Then by rotatingthe hand wheels m0; it is possibleto vary the position of sleeve ID I for: example, with reference to:link 153 and move the periphery: of. roll 6d. towards the pert...

V phery" of roll 63 for proper grinding. During this} adjustment springIU' lholds web- I508 against nut I016; The adjustment may be locked. bytightening hand wheel #02. As: millin pressure (i. e. the pressureexerted by the material: being ground) develops. this may be sufficientto. c'om:-= press: spring I 94 further and move the entire journal:Bflioutwardly from the vertical center line; of the machine and? along:rod 96. When this: occurs a clearance will develop between nut.- 1108;and web". me; To maintain a given fineness of? grind. a readjustment ofthe wheel I00 maybe re quired so as to change the position of journalwhile the mill is operating and the milling pres-= sure is on. In anyevent spring; I04 will com. press and permit hard obstacles to becleared by the rolls. In order tosmove the rolls 64 and 82 quickly awayfrom rolls 63. and: 6Il, respectively; handle 98- is moved in thedirection: of arrow 0 against left-hand stop-98. When. the handle 90moved in the direction of arrow MD, the entire bearing support 15isqui'c-kly moved towards the sidewall 13 of the machine by action ofeccentric 92 through link 94 and rod H4, and thus roll- 6-2 is. thusquickly moved away from roll 6.I- so to clear any: obstruction thatmayhave developed on that side of the machine and at the sametime bearingBills moved toward side wall M and roll 64 is moved away from roll 63.The bearin-gcomstruction on the far; end of the machine (plate H): isexactly analogous and by means of'its handlever, not illustrated, therolls 62. and 6 maybe quickly moved to clear position at that end;-Usually the hand levers at the two ends of the machine areconnectedtogether by linkages for simultaneous movement so that by pulling theleveron either end of the machine, the rolls may-- be quickly separated.Since the adjustments at the two ends of the machine are independent. itis possible to maintain accurately theuniform clearance between therolls 63 and 64, regardless of irregularities in operation of the mill.This is called tramm-ing, i. e. maintaining. the rolls parallel. Sincethe fixed, fast speed rolls BI and 63 of the present mill diagonallyoverlie" the ad-= justable slow-speed rolls 62 and; andtherolls B2 and64" are movable in a horizontal plane through the machine, much lesscritical parallel adjustment or tramming is required; as cornpared witholder mills in which the, rolls are on the same level. One of the handwheels III of the bearing support is' shown in Figure 1,, Iti'sunderstood that the bearin support 85 is; precisely the same as thatpreviously described for. bearing support 8|.

Likewise the shaft I4 carried on the bearing support 16 and thecorresponding bearing support. at the opposite end of the machinefor'shaft'll; are provided with adjusting hand wheels 'I I2- II3 whichpermits variation. in the closenessof the rolls and the pressure'necessaryto move the tension shaft attached to link 94 is illustratedat H4 and it extends through the housing H5 and terminates at wheel II2.Each end II and I2 is preferably provided with stops 98 for limiting themovement of lever 90 in its open and operating positions.

Within the machine housing there are provided adjustable baffles H6 andIll which serve to direct the downwardly falling material directly intothe nip ofeach pair of rolls 63-64 and 6I-62. The grain falls downwardlyfrom the feed rolls 32; and 33 in the general direction of arrows H8 andH9 and are directed by the boards -I I6 and III into the nip spacebetween the differentially revolving rolls.

r .The mechanism for rotating the rolls is illustrated in Figures 1 and2. The motor shaft 59 is provided with a spiral gear 60 mating with acorresponding spiral gear I26 on countershaft I2I'. The shaft [H issupported in a plurality ofbearings I22 and is therefore rotated by thegears 66 and I26 at approximately motor speed. Upon shaft I2I there is aherringbone gear I24 which mates with a corresponding herringbone gearI25 upon the countershaft I26 which is likewise'supported by thebearings I21. Since the gears I24 and I25 are approximately the samediameter the countershaft I26 is likewise rotated at approximately motorspeed. At the ends of the shaft I26 there are provided worm gears I28and I29 which mate, respectively, with the worm wheels. I36 and I3I onthe ends of roll shafts I6 and 65,'respectively'. The-gear pairs I28-I36and I26'I3i afford approximately a 1 to 1 gear ratio-and therefore therolls BI and 63 ,are rotated at approximately motor speed. By suitablyselecting the angle of the gears I28I36 and I 1I29 -I3I, the fast roll6! may be caused to rotate in the direction of arrow I32 and at the sametime fast roll 63 may be caused to rotate in the direction of arrow I33.With such rotation the countershaft I26 rotates in the direction ofarrow I34 and countershaft I2I rotates in the direction of arrow I35,the motor being rotated in the direction of arrow I46; The thrust causedby gears I28'and I28 reacted with gears I36 and I3I,- respectively, istherefore approximately balanced and relatively little end thrust istransmitted by shaft I26 to the bearings I2! in which it operates.

- Upon shaft I2! there are provided worm gears I36 and I31 of equaldiameter which mate with relatively larger worm wheels I38 and I39causing the latter and the roll shafts and rolls which they drive to berotated in the direction of arrows I46 and MI, respectively, but at amuch lower speed than the rotation of rolls 6| and 63. By appropriateselection of the gear ratio of the gear pairs I'36I38 and I3'II39, therolls 62 and 64 can be caused to rotate at any desired speed relativetothe speed of rolls 6| and B3 and accordingly the desired relativelyperipheral velocity for adequate grinding of various ma-. terials can bevaried to suit the conditions needed in the particular grindingoperation under cons'ideration. It will be noticed also that therotation of shaft I2I in the direction of arrow I35 causes the rotationof gears I36 and I39 in opposite directions. Therefore, the end thrustpro duced by each of the gears I36 and I3! upon III the shaft m issubstantially balanced. The only.

appreciable end thrust on this shaft is that produced by the gearsreacting against gear I20.

The gears I36 and I3! are made relatively long and since they are ofuniform pitch diameter throughout their length, they mate precisely withthe gears I38 and I39, respectively, regardless of the adjustmentposition of the latter gears as determined by the position of theirbearing blocks I5 and 86.. Therefore, the bearing blocks 15 and and thecorrespondingbearings at the opposite end of the machine may be moved bythe quickopening handle and their position maybe adjustedby the handwheels I66, I62, H2 and H3 and the correspondingadjustment wheels at theopposite end of the machine as desired, without disturbing the precisemating of the gears I36 and I31 with the corresponding gears I38 andI39, respectively. Furthermore, as the rolls are reduced in diameter asshown in Figures 4 and 5, thus requiring the closer together setting,depicted in Figure 5, this fact likewise does not effect the accuratemating of the gears I36 and I39 upon their driving gears I36 and I31,respectively, since the gears I38 and I39 simply operate at positions ongears I36 and I3! which are a little closer to the center of the mill. 7

Referring to Figures 4 and 5, particularly, the pressure caused by thegrinding of material between the rolls 6i and 62, for example, is in thedirection of arrows I42 and I43. The force of arrow I42 has an upwardcomponent I44 which therefore merely tends to lift the weight of theroll 6|, or stated another way the weight of the roll 6| tends tomaintain the milling pressure upon the cooperating roll 62. Similarly,the weight of roll 63 tends to maintain the milling pressure upon itscooperating roll 64. This is a distinct advantage as compared withearlier mills wherein the entire milling pressure had to be sustained bythe bearings carrying the roll shafts. In addition, the elimination ofthe drive belts and the provision of a geared drive reduces bearingpressure, permits the use of shorter shafts which consequently distortless under load. re-

duces fire hazard and employee hazard, and at the same time greatlyreduces vibration and the transmission of vibratory and belt stress tothe building carrying the mill.

Referring to Figure 1 the entire gear train for driving the rolls fromthe motor, together with the countershafts is preferably enclosed in asuitable gear housing shown by the dotted lines I45 which is suitablysupported from the end plate I2 of the mill. The housing has not beenshown in detail since it will be understood adequately to enclose thegears so as to permit their complete lubrication during operation.Likewise the bearings of the various countershafts are intended merelyas illustrative, it being understood that adequate bearing supports willbe provided on one or both sides of each gear in order to sustain theloads encountered during service. At the rear end of themill the shafts65 and i6 protrude outwardly beyond their hearing and are provided withV-belt pulleys I48 and I49 which serve to drive the belts I56 and I5Iand thus propel the material feed roll pulleys 38and 42, respectively.The feed rolls thus are operated at relatively low speeds whenever themill is in operation. The main housing of the mill and also the geardrive housing I45 are provided with removable sections which separatealong the planes I52, I53, I54 and I5 so as to permit the rolls 6 E454,their shafts and drive gears, to be lifted bodily from the mill forrenewal or replacement.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodiments hereinexcept as defined by the appended claims.

What I claim is:

1. A roller mill comprising a frame, a first pair of rollers positionedin an elevated transverse plane through the frame and substantiallysymmetrically about a vertical center plane through the frame, a secondpair of rollers journaled on the frame and positioned in a lowertransverse plane and more widely spaced than said first rollers fromsaid center plane, means for moving each of the second rollers towardand away from the center plane of the frame so as to position theperiphery of each of said second rollers closer or farther away from theposition of the more elevated first roller to which it is adjacent, afirst transverse countershaft journaled in the frame and worm gear meansconmeeting said shaft to each of the first pair of rollers, a secondtransverse countershaft journaled on the frame and worm gear meansconnecting said second shaft to each of said second pair of rollers, apower source on the frame and drive means connecting it to the first andsecond countershafts.

2. The apparatus of claim 1 further characterized in that the worm gearmeans connecting the first countershaft and the first pair of rollersdrives said first rollers in opposite directions and the worm gear meansconnecting the second countershaft to the second pair of rollers drivessaid second rollers in opposite directions.

3. The apparatus of claim 1 further characterized in that the powermeans is an electric motor having a gear connection to the secondcountershaft, said second countershaft being geared to the firstcountershaft.

4. A roller mill comprising an enclosing housing, a material feed chutehaving means therein for providing separated flows of grain to each of apair of spaced feed rolls cooperating therewith for feeding materialdownwardly in spaced planes extending substantially the length of thehousing, a pair of cooperating grinding rolls situated beneath each feedroll in the path of falling material fed thereby, each pair of grindingrolls comprising an elevated roll, journal means for said elevated roll,and a lower roll, journal means for said lower roll, said lower rollsbeing posi- 10 tioned beneath each feed roll and mounted for movement ina horizontal plane toward and away from its cooperating more elevatedslow roll through a range of movement sufficient to position theperipheries of the rolls in spaced relation or in grinding relationregardless of reduction of diameter of the cooperating rolls duringtheir service life, a first countershaft, worm gear means connecting thecountershaft to each of the slow rolls and a second countershaft, wormgear means connecting said second countershaft to each of the fastrolls, and a motor mounted on the housing and gear means connecting itto each of the countershafts.

5. The apparatus of claim 4 further characterized in that the motor ismounted within the housing in a ventilated enclosed space separated fromthe spaces below the cooperating pairs of rollers.

6. The apparatus of claim 4 further characterized in that the slowrollers are mounted on slidable journals and adjustment means isprovided at each end of the housing for moving them directly towards andaway from each other while gear connected to their countershaft drive.

THOMAS G. CE'CKA.

REFERENCES CITED The following references are of record in the file ofthis .patent:

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